In a conventional multi stage vacuum pump, the rotor assembly comprises two sets of rotor components that are each mounted on a respective one of two drive shafts. The shafts rotate to cause each of the rotor components to interact with a corresponding rotor component mounted on the other drive shaft. The coupling between the drive shaft and the rotor components is key to transmission of the torque therebetween.
One attachment method for coupling the rotor components to the drive shafts involves shrink fitting each rotor component onto a drive shaft. This method provides a secure way of anchoring the rotor component to the drive shaft so that rotation of the drive shaft results in very efficient transmission of the torque to the rotor component. However, if the rotor component deteriorates over time so that its replacement becomes necessary, separation of shrink fitted components can be difficult and time consuming.
An alternative attachment method involves providing a slot or key way into both the rotor component and the drive shaft at corresponding locations, positioning the rotor component on the drive shaft, aligning the rotor component and drive shaft keyways and inserting a key therein. Whilst this method may result in a rotor assembly that is easier to disassemble than that resulting from the aforementioned shrink fitting attachment method, the machining of the key ways is complex and introduces stress concentrators into both the rotor component and the drive shaft.
In each of the aforementioned methods of rotor attachment, angular and orthogonal alignment of the components is critical and not particularly straight forward. It is, therefore, desirable to provide a configuration of rotor component and rotor assembly of reduced complexity and which can be readily disassembled should the need arise.